Should I Keep the Pump Running Through Winter?

The question of whether or not to keep your koi pond's pump and filter running through the winter is one that many hobbyists ask this time of the year, although it can be difficult to give a straight answer. In general I would say yes, keep things running as they are but this depends greatly on the climate of where you live, the current weather and your pond/filter setup.

Koi are very adaptable and can cope with most climates, although extremes should be avoided. The water shouldn't be allowed to drop to below 4C for long, and rapid changes can be very stressful. This is one of the main reasons why people heat their ponds, not to keep them at summer temperatures, but to keep them stable. Of course people that choose to heat their koi ponds will leave their pumps and filters running, as often they will maintain the temperatures just high enough to continue light feeding. This usually requires that you keep the heat in with a pond cover to cut down on the fuel bills. A cover is also very useful even if you don't heat your pond just to keep out the worst of the winter weather and reduces wind chill.

As the temperatures reduce so does the activity of your koi and filter bacteria. Conversely dissolved oxygen levels increase, so with less demand below 8C aeration from fountains, waterfalls and air pumps can be switched off or diverted. In fact devices like this can actually chill the water further, one of the reasons trickle filters and Bakki showers have failed to take off in the UK. You may wish to keep air pumps running to your filter as moving water takes longer to freeze and it can help with re-establishing the bacteria come spring.

One of the main misconceptions about the design of a koi pond is that it should be very deep for the koi to survive over winter. A lot of this has come from garden pond and water garden advice where fish are kept in a much more natural environment and at lower densities. Most garden ponds are deep enough not to freeze solid, so the main reasons for a koi pond being so deep is its ability to support a greater quantity of fish and also provide more stable conditions. Experts talk about the stratification of water into different temperature layers due to the varying densities that are unique to water. It's because of this that it is suggested that koi move to the bottom of a pond because it is warmer but the truth is that koi sit on the bottom to conserve energy. What is being described is a thermocline where water as it gets colder gets heavier until it reaches it's maximum density at 4C. As it gets colder still it gets strangely less dense until it becomes ice, which we all know floats.

What this means is the bottom of your pond cannot be warmer than 4C before ice starts to form on the surface. On the other hand if you continue to circulate the water from the bottom to the surface the mixing can reduce the overall pond temperatures still further which is not good for your koi. As well as the temperature effect koi need to save energy through the winter months so are better off without having to swim against strong currents.

The answer then is when the water temperatures drop to 8C try to maintain it by reducing the exposure to the colder air by restricting the pump flow or use a smaller pump. You can make the water return to the pond by creating less splashing and it's also a good idea to lag the pipes. Submersible pumps in the pond can be raised if possible to leave the warmer water undisturbed. Years ago before filters were fed by bottom drains it was common to have a mid water intake and are very useful to have if you experience a harsh winter.

If the bottom temperature drops further to 4C then it's probably best to either switch off the pump or use a heater. If you do choose to switch off the pump then try to empty the pipes so there's no chance of them splitting if it does freeze. Don't worry if the pond does ice over as this normally won't cause any problems unless it stays like it for weeks and the pond is heavily stocked.

Pond Pump Failures

This weekend I decided to tidy up the shed and throw out any old koi stuff that I really should have gotten rid of years ago. For some reason I just seem to gather clutter and I know it's my own fault but I hate throwing things away if I think one day they may come in useful or I can fix them. The shelves were full of old pH test kits that may still work but it's best not to trust them. I find the pH test strips go off very quickly and give very unreliable results, so always renew them or double check the results if yours are getting on a bit.

I like to keep a few medications in case of emergencies but the shed was turning into a potential chemical disaster area and in some peoples eyes was resembling a bomb making factory, not that I know what one looks like of course. It's a good idea to have a small medical kit of treatments readily available for such times as a koi jumping out but they really should be replaced once the sell by dates have expired. Chemicals like Malachite Green and Formalin can be seriously damaging to your health if they leak and should always kept out of reach from children and pets. Knowing how to dispose of this stuff isn't easy but it's best not to throw them down the sink.



Amongst the tangle of pipes, tubes and plumbing supplies I have kept a collection of defunct pond pumps much like one keeps hunting trophies. To be honest all of these pumps had run beyond their expected lives but when you spend your money on a pond pump and it eventually dies my initial reaction isn't to bin it but hope that one day it can be repaired. I did manage to get the Pet Mate pump to work again but when it started eating impellers once a month it had to stop.

I always have a backup pump ready just in case of break downs but if you run an external pond pump then most of us aren't willing to buy a spare. External pond pumps are usually repairable anyway so I always keep a powerful submersible pump ready for such occasions. The photo on the right is of a pond pump I recently bought from my local Aldi supermarket for £25 which when rated at 3500 gallons per hour is unbelievably good value. From past experience these big sump pump type submersible pond pumps aren't cheap to run and I wouldn't trust this ones long term reliability, but it's great as a backup and very useful for emptying tanks fast.

Out of all the submersible pond pumps that I have owned the Oase pump has proved to be the best in terms of reliability, build quality and performance but in the end it died the same as the others. The newer ones maybe better but the biggest cause of pump failure that I have experienced has been due to the motor bearings wearing out. The manufacturers build these pumps with long lasting ceramic shafts which are fine but often the bearings wear out before the impeller does causing the seals to fail and eventually the motor burns out. I guess they will never build an everlasting pond pump as they make money on supplying replacements and the costs would be too great, so I suppose an average of five years is not worth complaining about.

My tip for buying a pond pump would be to check for the availability of spares as many dealers stock them, often in complete kits. It's probably best to buy them now than hope they are still available years later as new models are coming out all the time. Some pumps come complete with spare impellers o-rings and even shafts which can be handy but does tend to suggest that you will have to use them sometime in the future. An expensive pump should come with a longer warranty. If it doesn't then it's not worth the extra money. Even if the manufacturer is willing to fix the pump your pond will still be out of action in the mean time so it still makes sense to get a backup or two. Sometimes two smaller pumps can work out more effectively than one big one.